1. Field of the Invention
The present invention relates to a wireless LAN (Local Area Network) system, and more particularly to a wireless LAN system in which a base station and a wireless terminal device in a cell (wireless LAN domain) communicate to each other by using a spread spectrum system, a base station device and a wireless terminal device therefor, and a method for relaying an information frame.
2. Description of the Related Art
A wireless LAN system in which a base station and a wireless terminal device communicate to each other by using a spread spectrum system has been known.
A wireless LAN system in which a wired LAN is connected to the base station of such a wireless LAN system to allow intercommunication between the wireless terminal device and the wired LAN terminal device has also been known. Such a wireless LAN system is disclosed in JP-A-4-249443.
In the wireless LAN system which allows the interconnection of the wired LAN and the wireless LAN, it is necessary for the base station to determine whether a terminal which transmitted a user frame (information frame) is present in the wireless LAN or in the wired LAN and relay it to a designated destination terminal device.
For this purpose, a wireless LAN system which realizes the relay of the information frame by a bridge function has been proposed. Such a system is disclosed in IEEE Std 802.1D-1990 "Media Access Control Bridges", pp 31-47. Entry terminal information, that is, filtering database (FDB) is provided in the wireless LAN system to realize the bridge function. When the base station receives a user frame from the wireless LAN or the wired LAN, it stores a source address of the user frame in the FDB to identify whether the terminal which transmitted the user frame is present in the wireless LAN or in the wired LAN. When the base station receives a user frame, it compares a destination address thereof with the address registered in the FDB to relay or discard the user frame.
Namely, when the base station receives a new user frame from the wired LAN and the destination address has been registered as being present in the wired LAN, it discards the received frame, and if it has not been registered, the base station relays the received frame to the wireless LAN. Similarly, when the base station receives a new user frame from the wireless LAN and the destination address thereof has been registered as being present in the wireless LAN, it discards the received frame, and when it has not been registered, the base station relays the received frame to the wired LAN.
In this case, if a frame is transmitted from a non-registered terminal while a total number of addresses (specifically MAC (media access control) addresses) registered in the FDB in the base station has reached an upper limit of the total number of the MAC addresses registerable in the FDB in the base station, or if a frame is transmitted from a terminal which is not authorized to be registered in the FDB in the base station, the base station does not register the MAC address of that terminal in the FDB but discards the frame.
Accordingly, unless the same MAC address as the destination address of the user frame newly received from the wired LAN has been registered in the FDB of the wired LAN, the received frame is relayed whether or not the destination terminal is present in the wired LAN or the wireless LAN. Thus, when the destination terminal is not present in the wireless LAN, the wireless transmission line is wastefully occupied and a transmission efficiency of the wireless transmission line is lowered.
Further, when a wireless terminal device not registered in the FDB transmits a user frame to a terminal connected to the wired LAN, the frame is discarded by the base station and wasteful communication is conducted.
A terminal which is not authorized to be registered in the FDB in the base station cannot communicate with another terminal via the base station but it can communicate directly with another terminal in the same cell. In general, in the wireless LAN system, the communication between more than two terminals or between at least a terminal and a base station is permitted at a time within one cell. Accordingly, when a terminal not authorized for registration conducts the communication in the cell, normal terminal communication may be disturbed.